Whether it'd be an improvement for the coils would depend on what's on there now. My unlimited Mountain came with 17s and 58s, and that's built off a Sport platform. So in my case, paying anything to "swap" out to 17s and 58s would be pretty foolish.
It'd definitely be an improvement in the shocks. You'd go from hydraulic to gas. $70 would be a good price.
If you want more detail, read this (http://www.wranglerforum.com/f33/sus...ift-74282.html
) and the link within it, as well as the links within the link.